Theres no dof preview function because the camera is permanently in live view. So in effect you are already getting your depth of field preview by using the lcd screen or viewfinder. To get the same effect as the manual lens, all you have to do is go to aperture mode and choose the aperture you want. The bigger the aperture (smaller f number) the greater the depth of field. To get a shallower dof effect, go as close to the subject as possible and have the background as far as you can.